USE OF THE EURYHALINE BIVALVE POTAMOCORBULA-AMURENSIS AS A BIOSENTINEL SPECIES TO ASSESS TRACE-METAL CONTAMINATION IN SAN-FRANCISCO BAY

Potamocorbula amurensis was assessed as a biosentinel species in San F rancisco Bay, California, USA. Uptake of metal in both the laboratory and field showed that P. amurensis was sufficiently responsive to Ag, Cd, Cr, Ni and V to detect environmental differences in exposure; It w as less suitable as an indicator of Cu and Zn contamination. Concentra tion factors for P. amurensis were: Ag, 386 000; Cd, 50 200; Cr, 36 60 0; Cu, 12 200; Ni, 5200; and Zn, 115 500. Samples were collected from 6 stations throughout the bay at near-monthly intervals from January 1 991 to March 1992. Variability within a collection was influenced by g ut content and animal size. Other sources of variability were time [co efficient of variation (CV) = 10 to 21%], small-scale spatial variabil ity (within 3 km, CV = 10 to 25%), and large-scale spatial variability (CV = 3.3 to 12.4%). Depuration for 48 h was necessary to mitigate bi as from gut content. Precision was improved by analyzing large numbers of individuals (60 to 120) separated into several (5 to 14) composite s at each collection and by determining, from regression, the mean and variance for samples with significant correlations between metal conc entration and shell length. Repeated monthly sampling increased the ac curacy of long-term site characterizations. Temporal variability was s mall because of drought. The grand means of the concentrations of Ag, Cd, Cr, Ni, and V in the tissues of P. amurensis at each station for t he 15 mo period revealed persistent contamination from industrialized Suisun Bay to the mouth of San Francisco Bay. Demonstration of respons iveness, precision and accuracy should be a prerequisite for the optim al use of biosentinels.